1. Field of the Invention
This invention relates to a method of producing electro- or electroless-deposited film with a controlled crystal orientation and, in particular, to a method for controlling the crystal orientation in order to provide improved product properties.
2. Description of Related Art
A thin film is conventionally deposited and developed on a substrate by various deposition method, including a wet method such as electro- or electroless-deposition method, and a dry method such as sputtering method, PVD method, CVD method and the like. Among other things, in the wet method, a material (e.g., metal) in electrolytic solution assumes an ionic state and is deposed on a substrate to form a thin film by electro-deposition method or electroless-deposition method. In this instance, it is desirable to control the crystal orientation of the deposited film to improve the product property of the film. The crystal orientation of the deposited film is generally controlled by:
(1) orienting crystals of the deposited film into conformity with the crystal orientation of the substrate, or PA1 (2) subjecting the deposited film to stresses through the substrate, PA1 (3) controlling an overvoltage applied to the electro-deposition environment.
The method (1) above is generally known as epitaxial method, and requires no particular explanations. The method (2) above is usually seen when stresses are added to the substrate during the deposition process due to a difference in terms of the coefficient of thermal expansion between the substrate and the deposited film. Furthermore, the method (3) above utilizes a phenomenon wherein an easy axis of the crystals in the deposited material, in which electro-deposition tends to readily occur, changes depending upon the applied overvoltage. For example, in the case of an electro-deposited Zn film, the crystals of the deposited Zn film are oriented into the c-axis when the overvoltage is low, and into the a-axis or b-axis under an increased overvoltage.
Beside the above-mentioned methods (1), (2) and (3), there may be instances wherein the crystal orientation of the deposited film is controlled by controlling temperature of the substrate or the temperature or flow of the electrolytic solution, etc.
However, these methods suffer from a serious problem that they can be applied only to specific substances. Moreover, while the known method for developing the deposited film allows the development of a deposited film comprising crystals oriented in a thermodynamically stable direction, it is still difficult, if not impossible, to develop a deposited film comprising crystals which are oriented in other direction.